1. Field of the Invention
The invention described herein involves a multiple layer multileaf collimator for use during radiation treatment to shape and control the spatial distribution of a radiation beam.
2. Description of the Prior Art
During conventional radiation therapy treatment a radiation beam of varying angles and intensities is directed at a tumor in a patient. Typical treatment field shapes currently used (square, rectangular, or a modification thereof) result in a three-dimensional treatment volume which unfortunately includes segments of normal tissue and organs. The normal tissue and organs located in the path of the radiation beam must be taken into account for obvious safety reasons, thereby limiting the dose that can be delivered to the tumor. Cure rates for many tumors are a sensitive function of the dose they receive. The dose delivered to the tumor can be increased if the amount of exposed normal tissue or organs is reduced. Various methods of making the treatment volume conform more closely to the shape of the tumor volume are being developed, with the goal of delivering a higher dose to the tumor with less damage to normal tissue and organs, resulting in a positive effect on the health of the patient. Various approaches are being developed, including moving solid jaw-blocks during treatment, scanning the radiation beam over the volume to be treated, and using a multileaf collimator to create an irregularly shaped field related to the shape of the tumor.
Multileaf collimators can be used in a manner similar to conventional solid jaw-blocks. In addition, each individual segment or leaf in a multileaf collimator can be positioned independently, allowing the user to create an infinite amount of irregularly shaped fields. The radiation beam is directed between the ends of opposing arrays of the radiation blocking collimator leaves, thereby shaping the beam to closely match the shape of the desired treatment area, while shielding the normal tissue and organs.
U.S. Pat. No. 5,166,531 issued to Hunziger on Nov. 24, 1992 discloses a multileaf collimator arrangement positioned about the central axis of a radiation emitting head for shaping an emitted radiation beam. In place of the opposing solid jaw-blocks found in the standard collimator, one finds two opposing arrays of side-by-side elongated radiation blocking collimator leaves. Each leaf in each opposing array can be moved longitudinally towards or away from the central axis of the beam, thus defining a desired shape through which the radiation beam will pass.
Because the adjoining leaves must be tightly positioned side-by-side in order to minimize radiation leakage between the leaves, friction is an inherent problem, creating complications in maintaining a set position of one leaf while re-positioning an adjacent leaf, such repositioning being frequently required in conformal therapy. If friction between the adjacent leaves is reduced by providing a looser fit between adjacent leaves, unacceptable radiation leakage through spaces between the adjacent leaves will result. On the other hand, maintaining a tight leaf fit between the adjacent leaves and providing a teflon or other lubricating layer in the contact area of the adjacent leaves is also not an acceptable solution because the lower density of the lubricating layer, as compared to the high density of the collimator leaves, will allow an unacceptable amount of radiation leakage to occur.
It is an object of the present invention provide a multileaf collimator arrangement which not only solves the radiation leakage and friction problems mentioned above, but also improves the ability to accurately define the desired shape through which the radiation beam passes.
It is a further object of the invention to reduce the overall manufacturing cost of multileaf collimators.
It is an even further object of the invention to provide a multileaf collimator arrangement which maintains the ability to create larger rectangular treatment fields.